Photoelectric sound reproducer



, Feb.'10, 1942. Gfx.. DIMMICK PHOTOELECTRIC SOUND REPRODUCER Filed March 22, ,1940

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nventor Pnienied Feb. 1o, 1942- l Pno'rosLEcrRIc soUND REPRODUCER Glenn L. Dimmiek, Hnddenfield, N. J., assigner to Radio Corporation of America,

of Delaware a corporation Application Maren 2z, 1940, serial Nn. 325,313

4 Claims.

This invention relates to `a photoelectric sound reproducer of the sound on lm type, and more particularly to such an apparatus adapted to operate with a multiplex sound track. For some purposes, it is highly desirable to provide a plurality of simultaneously reproduced sound tracks. This is particularly so when the reproduced sound is to be controlled as to volume, distribution or other characteristics by means of a control track as set forth in Weinberger Patent No- 1,850,701 and Beers Patent No. 2,098,561, which disclose the use of one or more sound tracks and a control track. In such apparatusthere may be a dis? tinct control tone for each audio frequency track, and the amplitude of a particular control tone in the control track determines the amplitude of the reproduction of the spec-inc audio frequency tracklinvolved. Such systems broadly form no part of my invention which is directed more par- ;ticularly to the soundhead and optical system for directing light modulated by the various sound and control'tracks onto the photocells by which 'they are to be reproduced.

In the reproduction of a conventional sound track having a width of the order of 70 mils, it is comparatively simple to direct a small image of a slit upon the `film, .thereby producing a scanning line having a width of the-order of three-quarters of lenses onto the necessary width of the film. The' lens next preceding the film is a cylindrical lens of very short focal length which produces a sufliciently narrow line of light on the lm, as described and claimed in I -Iardy Patent No. 2,010,- 951. It is the length of the aperture immediately preceding this lens which determines the length of the line of light, while the focal length of the lens determines the width. The light from the illuminated area of the film is projected by an appropriate projection lens onto a series of cylindrical lenses corresponding in number with the number of half sound tracks to be reproduced,

or, rather with the number of photocell'cathodes on which the light is to be directed, and these cylindrical lenses direct eachportion of the beam to its appropriate cathode.

One object of the invention is to provide an improved multiplex sound reproducer.

Another object of the invention is to provide an improved manner of mounting an exciter lamp so as to avoid stray reflections..-

Another object of the invention is to provide an improved optical system for reproducing a multiplefsound track. e

Another object of the invention is to provide an improved form of light divider in sound reproof a mil or less and to direct the light passing through the lm onto a photocell.v Such optical systems are well known and customarily use a microscope objective or the like to focus the light on the iilm.

When the multiplex sound-tracks are used, it may be desirable to use push-pull tracks in which each half of a sound track carries a complete sound record or use what is known as classi B push-pull tracks in which the oppositehalf waves are recorded in adjacent tracks as described, for. example, in Dimmick Patent No. 2,093,423. Further, in the production of such multiple sound tracks, there is insuicient space. available on the standard motion pictureiilm and since a separate lrn is required, it becomes desirable to use the additional lm area most effectively. Thus assuming four tracks on a film having a clear width `of 1" between sprocket holes, the sound 'track widths may be doubled, giving a width for each sound track of the order of .140" to .160" and leaving adequate space between the f sound tracks.

ducers.

Another object of the invention is to provide an improvedrneans for collecting the light passing through a sound track and directing it onto the appropriate photocells.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the followingA speciflcation andan inspectionv of the accompanying drawing in Figure 1 is a side view of the optical system, that is, assuming that the film moves downwardly from the top tothe bottom of the sheet, and

Figure 2 is a topview corresponding to Fig. 1, in which the lm would move perpendicularly to the plane of the paper.

Referring first to Fig. 1, the light source consists of the usual incandescent exciter lamp having a coil filament I0 and a tubular envelope I I.

' The faces of the tubular envelope reilect a conthe envelope inclined at an angle to avoid bulb reflections and the light is condensed by a group siderable quantity of light, which may amount to as much as 8 or 10 percent, and, in order to.

prevent this reected light from passing .through the optical system and possibly aecting the denition of the image, I tilt the exciter lamp at an angle of possibly 30 to 45 from the perpendicular tothe optical axis, asv shown, so that any reections from the back of the envelope are directed completely outside -the path of light from the iilament through the optical system. Light to increase the size of the iilament on the lm.

The light emerging from the lens I3 passes through the cylindrical condenser IIl, which di rects it through the aperture in the plate I 5. This cylindrical condenser Ill is of such power as to direct substantially all the light passing through the aperture I 5 into the anastigmatic projection lens Il. Between the aperture plate Iii and the lm there is located a cylindrical lens IG of very short focal length. The focal length of this lens is sufciently short so that the image of the filament Il] which is formed by it 'on the iilm F has a width of the order of 1 mil or less, as described in the Hardy patent referred to above, and this fine line of light serves to scan the sound track on the llm passing therethrough.

After emerging from the 'lm, the light passes through the projection lens I'I and the cylindrical lens I8 onto the series of cylindrical lenses i9. The projection lens ii is of such focal length that if the cylindrical lens I is omitted, a series of images of the sound tracks 'on the nlm F are formed on the splitting cylinders I9, and these cylinders then cause the light to converge on the several photocell cathodes as indicated at 2i and 22 in Fig. 2. The cylindrical lens IB has no eiect in the horizontal plane and, accordingly, does not interfere in any way with the projection of the images of the sound tracks on the lenses i9 nor with their directing the light on the cathodes of the photocells 2G. The cylindrical lens I8, since it has its axis horizontal, causes the light to converge, as shown in Fig. l, to a horizontal line before it reaches the cylinders I9 and the light diverges from the said line through the cylinders iii to the cathode oi the photocells 2li, thereby'coveringl a large portion of the cathode length ofthe photocells as shown in Fig. 1.

It will be apparent that although I have shown four pushpull photocells which would operate with eight push-pull sound tracks, the invention is not limited to such an arrangement, but eight single sound tracks might be used with the same arrangement and a larger or smaller number of photocells may be used as desired. A1soas many or as few of these tracks as desired may be used as control tracks, or all may be used as sound tracks according to the purpose of the particular apparatus.

It will be also apparent that a tilted exciter lamp is not limited to use in a sound reproducer, but it may be used in sound recording apparatus or in any other analogous optical apparatus where it is necessary to avoid reiiections from the envelope of a light source.

Having now described my invention, I claim:

l. In an optical system for sound reproduction from a plurality of sound tracks on a film movable with respect to a translation point, means for illuminating the film at said translation point, means for directing an image of the sound tracks on the lm onto a plurality of cylindrical lenses, and means for dispersing said images longitudinally of said cylindrical lenses.

2. In an optical system for sound reproduction from a plurality of sound tracks on a lm movable relatively to a translation point, means for illuminating the illm at said translation point, means for directing an image of the sound tracks on the lm onto a plurality of cylindrical lenses, means for dispersing said images longitudinally of said cylindrical lenses, and photocells having their cathodes located to receive the beams passing through said cylindrical lenses.

3. In an optical system for sound reproduction from a plurality of sound tracks on a lrn movable relatively to a translation point, means including a cylindrical lens of short focal length adjacent the film for illuminating the lm at said translation point, means for directing an image of Ithe sound tracks on the film onto a plurality of cylindrical lenses, `means for dispersing said images longitudinally of said cylindrical lenses, and means for directing light through said cylindrical lens into the said image forming means.

Il. In an optical system for sound reproduction from a plurality of sound tracks on a lm movable relatively to a translation point, means for illuminating the film at the translation point. a projection lens forming images of the sound tracks on the lm on a plurality of cylindrical lenses, means for dispersing said images longitudinally of said cylindrical lenses, said means for directing the light on the lm including a cylindrical lens of short focal length adjacent the film, and means for directing light through said cylindrical lens into the said image forming means.

GLENN L. DIMMICK. 

